The invention relates to a pyrotechnic gas generator.
An arrangement for the multi-stage ignition of a pyrotechnic gas generator for passive restraint systems in motor vehicles is known from the generic EP 0 773 145 A2. The gas generator consists of two charging chambers independent of each other, in each of which fuel is contained and to which a respective ignition unit is assigned. These ignition units are to be ignited independently of each other. Both charging chambers are connected to a common expansion chamber.
The object underlying the invention is to design a pyrotechnic gas generator in such a way that, with small size and little weight, all in all low manufacturing costs are achieved. In this respect firing from the expansion chamber over into the individual charging chambers is to be prevented.
In accordance with the invention, the object is achieved in that a common cover constructed as a membrane is arranged between the charging chambers and the expansion chamber, in that a first perforated sheet-metal disc is arranged in each charging chamber, on which disc the cover rests, and in that a second perforated sheet-metal disc is arranged outside the charging chambers directly above the cover, with the cover being clamped between the first and second perforated sheet-metal discs, and in that smaller perforations are arranged in the first perforated sheet-metal disc than in the second perforated sheet-metal disc.
The claimed sandwich construction of the first perforated sheet-metal discxe2x80x94membranexe2x80x94the second perforated sheet-metal disc, with the larger perforations in the second perforated sheet-metal disc, has the advantage that, with a certain operating pressure in the charging chambers, the membrane is perforated and the gas vapours of the fuel can be sent to the expansion chamber. However, an unintentional firing from the expansion chamber over into the charging chamber is not possible if the thickness of the membrane is dimensioned in such a way that it is not opened at the relatively small perforations of the first perforated sheet-metal disc.
In a preferred embodiment the perforations in the first perforated sheet-metal disc have a diameter between 1 mm and 5 mm, the perforations in the second perforated sheet-metal disc a diameter between 6 mm and 10 mm and the cover or the membrane has a thickness greater than 0.1 and up to 0.5 mm. However, other values can also be meaningful here. If, for example, the cover or the membrane is thicker than 0.1 to 0.5 mm, then the diameter of the perforations in the two perforated sheet-metal discs must likewise be enlarged.
However, it is important that it is possible to open the cover from xe2x80x9cthe insidexe2x80x9d, that is to say from the charging chamber, but not from an expansion chamber into the charging chamber.
Advantageously, the charging chambers are arranged in a one-part charging container, with the base of the charging container being constructed as a generator structure. This means that the base is more stable than the side walls.
In order to avoid a firing from one charging chamber over into the other, a groove is preferably arranged in the walls of the charging chambers or in the charging container, in which groove the cover is supported in a form-locking manner. For a better hold, advantageously an additional clamping element, for example a ring, is inserted into the groove. This clamping element can even be welded in or glued in, for example. For the further improvement of the sealing, the cover is preferably constructed with the wall of the charging chambers or with the charging container as a flange, that is to say it is flanged. As a result of these measures a labyrinth seal is created. According to requirements, the groove can even be placed around only one charging chamber.
Ignition units are inserted in the base of the charging container, preferably projecting into the charging chambers. For this purpose, the floor can be appropriately curved inwards or the ignition units are inserted by way of a sealing element.
The charging container is, according to the invention, surrounded by a housing which is connected to the charging container by means of clinching and/or flanging.
The charging container preferably consists of aluminium and is manufactured by the extrusion method.
The expansion chamber is meaningfully connected to a filter area concentrically encompassing the charging container, and the filter area is connected to an air pocket via openings and in this way forms an air bag.